Well,they are three types of amps,basically,solid-state,tube,and digital. Tube amps,are stored with tubes while solid-state are mainly transistor based. Digital on the other hand is based on tones from famous amp's/effects incoporated into the digital amp itself.
Solid-state is rather dry sounding,whereas tube distortion sounds warm.
Nowadays,due to the number of amps around,most of us don't know wether which amp is which. Haha.